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DSS Images Other Images
Ýlgili Makaleler
Mid-infrared images of β Pictoris and the possible role of planetesimal collisions in the central disk
When viewed in optical starlight scattered by dust, the nearly edge-ondebris disk surrounding the A5V star β Pictoris (distance 19.3pcref. 1) extends farther than 1,450AU from the star. Its large-scalecomplexity has been well characterized, but the detailed structure ofthe disk's central ~200-AU region has remained elusive. This region isof special interest, because planets may have formed there during thestar's 10-20-million-year lifetime, perhaps resulting in both theobserved tilt of 4.6 degrees relative to the large-scale main disk andthe partial clearing of the innermost dust. A peculiarity of the centraldisk (also possibly related to the presence of planets) is the asymmetryin the brightness of the `wings', in which the southwestern wing isbrighter and more extended at 12µm than the northeastern wing.Here we present thermal infrared images of the central disk that implythat the brightness asymmetry results from the presence of a brightclump composed of particles that may differ in size from dust elsewherein the disk. We suggest that this clump results from the collisionalgrinding of resonantly trapped planetesimals or the cataclysmic break-upof a planetesimal.
| Dust-enshrouded giants in clusters in the Magellanic Clouds
We present the results of an investigation of post-Main Sequence massloss from stars in clusters in the Magellanic Clouds, based around animaging survey in the L'-band (3.8 μm) performed with the VLT at ESO.The data are complemented with JHKs (ESO and 2MASS) andmid-IR photometry (TIMMI2 at ESO, ISOCAM on-board ISO, and data fromIRAS and MSX). The goal is to determine the influence of initialmetallicity and initial mass on the mass loss and evolution during thelatest stages of stellar evolution. Dust-enshrouded giants areidentified by their reddened near-IR colours and thermal-IR dust excessemission. Most of these objects are Asymptotic Giant Branch (AGB) carbonstars in intermediate-age clusters, with progenitor masses between 1.3and ~5 M_ȯ. Red supergiants with circumstellar dust envelopes arefound in young clusters, and have progenitor masses between 13 and 20M_ȯ. Post-AGB objects (e.g., Planetary Nebulae) and massive starswith detached envelopes and/or hot central stars are found in severalclusters. We model the spectral energy distributions of the cluster IRobjects, in order to estimate their bolometric luminosities andmass-loss rates. The IR objects are the most luminous cluster objects,and have luminosities as expected for their initial mass andmetallicity. They experience mass-loss rates in the range from a few10-6 up to 10-4 M_ȯ yr-1 (ormore), with most of the spread being due to evolutionary effects andonly a weak dependence on progenitor mass and/or initial metallicity.About half of the mass lost by 1.3-3 M_ȯ stars is shed during thesuperwind phase, which lasts of order 105 yr. Objects withdetached shells are found to have experienced the highest mass-lossrates, and are therefore interpreted as post-superwind objects. We alsopropose a simple method to measure the cluster mass from L'-band images.
| Period-luminosity relation for M-type semiregular variables from Hipparcos parallaxes
We have studied the period-luminosity (P-L) relationships of oxygen-richsemiregular (SR) variables in several wavelength bands using Hipparcosparallaxes with an accuracy of better than 10 per cent. We have shownthat there is a clear dependence on period of absolute magnitude in theU,B,V,R,IC,J,H,K,L,M,N, [12], [25], [60] and [100] bands, andthat the slope of the linear Mλ- logP relation is asmooth function of wavelength. We point out that this relation can inprinciple be used to derive absolute bolometric magnitude as a functionof period.The behaviour of the second periods of SR variables in the P-L relationin the V and K bands is also discussed.
| Multiwavelength visibility measurements of Miras: observations of R Dor and R Leo with MAPPIT
We present interferometric visibility measurements of the nearbyMira-like star R Doradus and the Mira R Leo taken over a wide range ofwavelengths (650-990 nm). These are the first simultaneous observationsof visibility as a function of wavelength over such a wide wavelengthrange for a Mira. The observations were made using MAPPIT (MaskedAPerture-Plane Interference Telescope), an interferometer operating atthe 3.9-m Anglo-Australian Telescope. We used a slit to mask thetelescope aperture and a prism to disperse the interference pattern inwavelength. We observed in both stars strong decreases in visibilitywithin the TiO absorption bands across the observed wavelength range.Comparison of our results with theoretical models shows generalagreement but differences in detail, suggesting that further work isneeded to refine the theoretical models. We find that models for starspulsating in the fundamental mode best fit our observations.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| CCD Speckle Observations of Binary Stars from the Southern Hemisphere. II. Measures from the Lowell-Tololo Telescope during 1999
Speckle observations of 145 double stars and suspected double stars arepresented and discussed. On the basis of multiple observations, a totalof 280 position angle and separation measures are determined, as well as23 high-quality nondetections. All observations were taken with the(unintensified) Rochester Institute of Technology fast-readout CCDcamera mounted on the Lowell-Tololo 61 cm telescope at the Cerro TololoInter-American Observatory during 1999 October. We find that themeasures, when judged as a whole against ephemeris positions of binarieswith very well-known orbits, have root mean square deviations of1.8d+/-0.3d in position angle and 13+/-2 mas in separation. Elevendouble stars discovered by Hipparcos were also successfully observed,and the change in position angle and/or separation since the Hipparcosobservations was substantial in three cases.
| The Onset of Pulsation in Red Giants
The Hippercos astrometric and photometric database has many applicationsfor undergraduate research projects. As one example, we haveinvestigated the onset of variability in red giants by noting the excessscatter (above and beyond the instrumental scatter) in the Hipparcosphotometric measurements of 7600 giants with +1.35 < (V-I) <+1.70. Microvariability (0.00 < deltaV < 0.01) sets in graduallyfor (V-I) > + 1.55. These are, however, reddened colors, but thesmall contamination by distant reddened supergiants may be offset by thecontamination by reddened earlier-type giants. According to three recenteffective temperature scales, these two (V-I) colors correspond to 4085K and 3905 K, respectively, with an internal uncertaintly of +/- 10 K.
| Complex Structure of η Carinae in the Mid-Infrared
We report high angular resolution observations of complex mid-infrared(4.8-18 μm) structure in the η Carinae Nebula. This massive (~120Msolar), luminous star is surrounded by a large bipolarnebula extending as much as ~22" in the mid-infrared. Our observationsreveal the presence of several condensations within the complex coreknown as the Homunculus, as well as what may be a toroidal structurevisible at 18 μm. This structure may be related to a similar torusseen at near-infrared wavelengths. Our high angular resolutionphotometry reveals for the first time the spatial variation of thesilicate feature in the nucleus of the η Car Nebula. Finally, wepresent the first high-resolution mid-infrared color-temperature andoptical depth maps for the nebula and discuss their significance inrelation to the origin of the emission and evolutionary status of thestar.
| Stellar radii of M giants
We determine the stellar radii of the M giant stars in the Hipparcoscatalogue that have a parallax measured to better than 20% accuracy.This is done with the help of a relation between a visual surfacebrightness parameter and the Cousins (V - I) colour index, which wecalibrate with M giants with published angular diameters.The radii of(non-Mira) M giants increase from a median value of 50 R_Sun at spectraltype M0 III to 170 R_Sun at M7/8 III. Typical intermediate giant radiiare 65 R_Sun for M1/M2, 90 R_Sun for M3, 100 R_Sun for M4, 120 R_Sun forM5 and 150 R_Sun for M6. There is a large intrinsic spread for a givenspectral type. This variance in stellar radius increases with latertypes but in relative terms, it remains constant.We determineluminosities and, from evolutionary tracks, stellar masses for oursample stars. The M giants in the solar neighbourhood have masses in therange 0.8-4 M_Sun. For a given spectral type, there is a close relationbetween stellar radius and stellar mass. We also find a linear relationbetween the mass and radius of non-variable M giants. With increasingamplitude of variability we have larger stellar radii for a given mass.
| Supplementary southern standards for UBV(RI)c photometry
We present UBV(RI)c photometry for 80 southern red and blue stars foruse as additional standards. The data are tied to the Johnson UBV andCousins (RI)c systems and extend the range of the available stars forcolor equation determination, especially in (U-B) for blue stars and(V-R) and (V-I) for red stars. Comparisons with published data are madeand particularly good agreement is found with Bessell for the red(Gliese) stars.
| Obscured Asymptotic Giant Branch stars in the Magellanic Clouds. IV. Carbon stars and OH/IR stars
We present N-band photometry for a sample of 21 dust-enshrouded AGBstars in the Large Magellanic Cloud, and three additional sources in theSmall Magellanic Cloud. Together with near-infrared photometry, this isused to give a tentative classification into carbon and oxygen-richatmospheres. Bolometric luminosities are also estimated for these stars.In addition, we present the results of a survey for OH masers in theLMC, which resulted in the discovery of OH maser emission fromIRAS04407-7000. Spectra between 600 and 1000 nm have been obtained fortwo heavily obscured AGB stars in the LMC, confirming them to be highlyreddened very late M-type giants. Because the dust-enshrouded stars areclearly undergoing heavy mass loss they are assumed to be very near thetermination of their respective Asymptotic Giant Branch phases. Thefraction of mass-losing carbon stars decreases with increasingluminosity, as expected from Hot Bottom Burning. The best candidatecarbon star, with M_bol ~ -6.8 mag, is the most luminous mass-losingcarbon star in the Magellanic Clouds, and amongst the most luminous AGBstars. At lower luminosities (M_bol ~ -5 mag) both oxygen and carbonstars are found. This may be explained by a range in metallicity of theindividual mass-losing AGB stars. based on observations obtained at theEuropean Southern Observatory (La Silla, Chile: proposal ESO 54.E-0135),the South African Astronomical Observatory, and the Australia TelescopeNational Facility
| R Doradus: the biggest star in the sky.
Not Available
| The angular diameter of R Doradus: a nearby Mira-like star
We find the angular diameter of R Doradus to be 57+/-5mas, exceedingthat of Betelgeuse and implying that R Dor is larger in apparent sizethan every star except the Sun. R Dor is shown to be closely related tothe Mira variables. We estimate an effective temperature of 2740+/-190K,a distance of 61+/-7pc, a luminosity of 6500+/-1400 Lsolar and a radiusof 370+/-50 Rsolar. The characteristics of R Dor are consistent with itbeing near the edge of a Mira instability strip. We detect non-zeroclosure phases from R Dor, indicating an asymmetric brightnessdistribution. We also observed W Hydrae, a small-amplitude Mira, forwhich we find an angular diameter of 44+/-4mas.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| Obscured asymptotic giant branch stars in the Magellanic Clouds - II. Near-infrared and mid-infrared counterparts
We have carried out an infrared search for obscured asymptotic giantbranch (AGB) stars in the Magellanic Clouds. Fields were observed in thevicinity of IRAS sources with colours and flux densities consistent withsuch a classification. The survey uncovered a number of obscured AGBstars as well as some supergiants with infrared excess. We presentphotometry of the sources and discuss the colour diagrams and bolometricluminosities. One of the supergiants is close to the maximum luminosityallowed for red supergiants, implying a progenitor mass around 50M_solar. Its late spectral type (M7.5) is surprising for such a massivestar. Most of the AGB stars are luminous, often close to the classicallimit of M_bol=-7.1. To determine whether the stars are oxygen-rich, wehave acquired narrow-band mid-infrared photometry with the ESO TIMMIcamera for several sources. All but one are found to show the silicatefeature and therefore to have oxygen-rich dust; the colours of theremaining source are consistent with either an oxygen-rich or acarbon-rich nature. A method to distinguish carbon and oxygen starsbased on H-K versus K-[12] colours is presented. We discuss severalmethods of calculating the mass-loss rate: for the AGB stars themass-loss rates vary between approximately 5x10^-4 and 5x10^-6 M_solaryr^-1, depending on the assumed dust-to-gas mass ratio. We present a newway to calculate mass-loss rates from the OH maser emission. We find noevidence for a correlation of the mass-loss rates with luminosity inthese obscured stars. Nor do the mass-loss rates for the LargeMagellanic Cloud (LMC) and Small Magellanic Cloud (SMC) stars differ inany clear systematic way from each other. Expansion velocities appear tobe slightly lower in the LMC than in the Galaxy. Period determinationsare discussed for two sources: the periods are comparable to those ofthe longer-period Galactic OH/IR stars. All of the luminous stars forwhich periods are available have significantly higher luminosities thanpredicted from the period-luminosity relations.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| On the spectra and photometry of M-giant stars
From a sample of 97 very bright M-giant stars in the Solarneighbourhood, high-quality "intrinsic" spectra in the spectral range380 <~ λ[nm] <~ 900 for all M-spectral subtypes of the Caseand MK classification systems are obtained. The results are fitted tophotospheric synthetic spectra in the range 99 <~ λ [nm]<=12500 in order to infer the corresponding continua. The syntheticspectra are also compared to the intrinsic spectra. The effectivetemperatures are derived and mathematical spectral classificationcriteria are found. The (UB)_j_(VRI)_c_(JHKLM)_ESO_ photometric data ofthe sample are also given. The data are available on the StrasbourgAstronomical Data Centre (CDS).
| Asymptotic giant branch stars near the sun
Available red and near-infrared photometry and apparent motions of M, S,and C asymptotic giant branch (AGB) stars in the Bright Star Catalogueare tabulated and discussed. It is shown that the red and near infraredindices normally used for late-type stars are interchangeable except forcarbon stars. The M-type giants are variable with visual amplitudegreater than 0.05 mag. The reddening-free parameter m2 from Genevaphotometry is essentially a temperature parameter for M giants, whilethe reddening-free parameter d is a sensitive detector of blue stellarcompanions. The space density of AGB stars near the sun decreases by afactor of 35 in a temperature range 3800 to 3400 K. Two of the S starsnear the sun were found to have nearly equal space motions and may becomembers of the Arcturus group.
| M Giant Populations and Galactic Structure
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.247..227F&db_key=AST
| Southern JHKL standards
The basis for the current SAAO standard photometric system at JHKL isgiven. This depends on an extensive investigation involving 230 starsdistributed around the sky. The accuracy is estimated at + or - 0.02 magfor J, H and K and + or - 0.05 mag for L.
| Infrared photometry and spectrophotometry of SN 1987A. I - March to October 1987 observations
IR (1-20 micron) observations, photometry, and narrow bandspectrophotometry of SN 1987A obtained between March 16 and October 12,1987, are presented. Variations of the bolometric luminosity aredetermined from IR and optical photometry. The spectral energydistribution, effective radius, and effective temperature of the hottercomponent are derived. Also, observations of hydrogen lines and COemission are discussed.
| Stellar integrated fluxes in the wavelength range 380 NM - 900 NM derived from Johnson 13-colour photometry
Petford et al. (1988) have reported measured integrated fluxes for 216stars with a wide spread of spectral type and luminosity, and mentionedthat a cubic-spline integration over the relevant Johnson 13-colormagnitudes, converted to fluxes using Johnson's calibration, is inexcellent agreement with those measurements. In this paper a list of thefluxes derived in this way, corrected for a small dependence on B-V, isgiven for all the 1215 stars in Johnson's 1975 catalog with completeentries.
| Intermediate-infrared excesses of barium stars
Some barium stars show large excesses at 10 microns. These excessesappear unrelated to other atmospheric broadband characteristics, and arestrongly indicative of circumstellar dust. This supports theories thatprevious mass transfer in an evolved binary system may be responsiblefor their spectral peculiarities. Spectral energy distributions ofbarium stars indicate that other broadband peculiarities are likely asfollows: strong deficiencies exist in the regions of the B and Ifilters, while weak excesses appear in the H and M spectral regions.These peculiarities appear to correlate with the barium intensity.Energy exceses are insufficient to balance deficiencies unless either(1) the V band itself represents an excess, or (2) there are additionalexcesses at shorter wavelengths. The precise atmospheric phenomenonleading to such deviation from a blackbody spectral distribution isunknown.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| The brightest high-latitude 12-micron IRAS sources
The Infrared Astronomical Satellite (IRAS) Point Source catalog wassearched for sources brighter than 28 Jy (0 mag) at 12 microns withabsolute galactic latitude greater than 30 deg excluding the LargeMagellanic Cloud. The search resulted in 269 sources, two of which arethe galaxies NGC 1068 and M82. The remaining 267 sources are identifiedwith, or have infrared color indices consistent with late-type starssome of which show evidence of circumstellar dust shells. Seven sourcesare previously uncataloged stars. K and M stars without circumstellardust shells, M stars with circumstellar dust shells, and carbon starsoccupy well-defined regions of infrared color-color diagrams.
| The optical properties of dust in the mid-IR silicate bands
A study of the emission silicate features of 10 supergiants and S Lep,which are all in the solar region of the Galaxy, is discussed. Theoptical efficiency of the circumstellar grain material of M stars isdeduced over the range 8-30 microns. It is shown that the efficiencyclearly peaks at 10 microns and is analogous to that of amorphousMg2SiO4. A similar procedure, using 13 available spectra of protostellarobjects, shows that the dust in molecular clouds and in the ISM, iscomposed of small (less than 1 micron) grains with an optical extinctionefficiency peaking at 9.5 microns and practically identical to that ofamorphous MgSiO3. Combining the two kinds of dust, and allowing forgrain sizes greater than 1 micron, it is possible to reproduce the wide10-micron features emitted by M giants with more or less thick shells.Using the results of meteoritic chemical analysis and of the theory ofcomposite gas condensation, the likelihood of amorphous MgSiO4 andMgSiO3 being present in circumstellar and interstellar dust,respectively, is evaluated.
| Stellar chromospheres - H-alpha and CA II K profiles
A set of medium to high-resolution observations of H-alpha and Ca II Klines in a sample of Population I stars is presented in order to examinethe systematics of H-alpha absorption profiles and to determineempirically the extent to which velocity fields observed therein arereflected in the chromospheric component of the Ca II line. Formain-sequence stars, bright Ca II K emission profiles accompany shallowH-alpha lines with sharp central cores, unlike the apparently U-shapedH-alpha cores of stars displaying relatively weak Ca II K emission. Forgiants and supergiants, the H-alpha line is generally wider than acomputed LTE photospheric profile, with significant K(3) absorptionpresent in the Ca II K(2) reversal profile. The excess widths appear tocorrelate with the strength of the K(3) absorption. Estimates of thestrength of Ca II K(3) indicate severe modifications of Ca II K(2)widths and intensities, strongly affecting the cooling role of Ca II Kin the upper chromospheres.
| Near infrared photometry. I - Homogenization of near-infrared data from southern bright stars
A single homogeneous data set containing near-infrared (JHKLM)photometry of bright stars in the Southern Hemisphere obtained fromdifferent sources is constructed based on the use of the Johnson systemas a standard. Data for 203 stars in the J, H, K and L bands and 87stars in the M band from the lists of Glass (1974), Engels et al.(1981), Wamsteker (1981) and Allen (1981, 1982) was combined bycomparison with the list of Johnson, followed by transformation into theJohnson J and K bands, the H band of Glass and Allen, an L band similarto that of Johnson but having the zero point of Glass, and the M band ofEngels. Average colors and spectral types are also obtained. The presentlist may be used to provide calibration objects in the range 1.2 to 5microns covering a wide range in color and brightness.
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| Sað Açýklýk: | 04h00m53.80s |
| Yükselim: | -62°09'34.0" |
| Görünürdeki Parlaklýk: | 4.51 |
| Uzaklýk: | 150.376 parsek |
| özdevim Sað Açýklýk: | 1.7 |
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